Thermocouples are suitable for measuring over a
large temperature range, up to 2300 °C. They are less suitable for
applications where smaller temperature differences need to be measured
with high accuracy, for example the range 0–100 °C with 0.1 °C accuracy.
For such applications thermistors and resistance temperature detectors
are more suitable. Applications include temperature measurement for
kilns, gas turbine exhaust, diesel engines, and other industrial
processes.
Types
Certain combinations of alloys have become popular as industry
standards. Selection of the combination is driven by cost, availability,
convenience, melting point, chemical properties, stability, and output.
Different types are best suited for different applications. They are
usually selected based on the temperature range and sensitivity needed.
Thermocouples with low sensitivities (B, R, and S types) have
correspondingly lower resolutions. Other selection criteria include the
inertness of the thermocouple material, and whether it is magnetic or
not. Standard thermocouple types are listed below with the positive
electrode first, followed by the negative electrode.
K
Type K (chromel–alumel) is the most common general purpose
thermocouple with a sensitivity of approximately 41 µV/°C, chromel
positive relative to alumel. It is inexpensive, and a wide variety of
probes are available in its −200 °C to +1350 °C range. Type K was
specified at a time when metallurgy was less advanced than it is today,
and consequently characteristics vary considerably between samples. One
of the constituent metals, nickel, is magnetic; a characteristic of
thermocouples made with magnetic material is that they undergo a step
change in output when the magnetic material reaches its Curie point
(around 354 °C for type K thermocouples).
E
Type E chromel constantan has a high output (68 µV/°C) which makes it
well suited to cryogenic use. Additionally, it is non-magnetic.
J
Type J (iron–constantan) has a more restricted range than type K (−40
to +750 °C), but higher sensitivity of about 55 µV/°C. The Curie point
of the iron (770 °C) causes an abrupt change in the characteristic,
which determines the upper temperature limit.
N
Type N (Nicrosil–Nisil) (Nickel-Chromium-Silicon/Nickel-Silicon)
thermocouples are suitable for use at high temperatures, exceeding
1200 °C, due to their stability and ability to resist high temperature
oxidation. Sensitivity is about 39 µV/°C at 900 °C, slightly lower than
type K. Designed to be an improved type K, it is becoming more popular.
Platinum types B, R, and S
Types B, R, and S thermocouples use platinum or a platinum–rhodium
alloy for each conductor. These are among the most stable thermocouples,
but have lower sensitivity than other types, approximately 10 µV/°C.
Type B, R, and S thermocouples are usually used only for high
temperature measurements due to their high cost and low sensitivity.
- B
Type B thermocouples use a platinum–rhodium alloy for each conductor.
One conductor contains 30% rhodium while the other conductor contains
6% rhodium. These thermocouples are suited for use at up to 1800 °C.
Type B thermocouples produce the same output at 0 °C and 42 °C, limiting
their use below about 50 °C.
- R
Type R thermocouples use a platinum–rhodium alloy containing 13%
rhodium for one conductor and pure platinum for the other conductor.
Type R thermocouples are used up to 1600 °C.
- S
Type S thermocouples are constructed using one wire of 90% Platinum
and 10% Rhodium (the positive or "+" wire) and a second wire of 100%
platinum (the negative or "-" wire). Like type R, type S thermocouples
are used up to 1600 °C. In particular, type S is used as the standard of
calibration for the melting point of gold (1064.43 °C).
T
Type T (copper–
constantan)
thermocouples are suited for measurements in the −200 to 350 °C range.
Often used as a differential measurement since only copper wire touches
the probes. Since both conductors are non-magnetic, there is no Curie
point and thus no abrupt change in characteristics. Type T thermocouples
have a sensitivity of about 43 µV/°C.
C
Type C (tungsten 5% rhenium – tungsten 26% rhenium) thermocouples are
suited for measurements in the 0 °C to 2320 °C range. This thermocouple
is well-suited for vacuum furnaces at extremely high temperatures. It
must never be used in the presence of oxygen at temperatures above 260
°C.
M
Type M thermocouples use a nickel alloy for each wire. The positive
wire contains 18% molybdenum while the negative wire contains 0.8%
cobalt. These thermocouples are used in vacuum furnaces for the same
reasons as with type C. Upper temperature is limited to 1400 °C. It is
less commonly used than other types.
Chromel-gold/iron
In chromel-gold/iron thermocouples, the positive wire is chromel and
the negative wire is gold with a small fraction (0.03–0.15 atom percent)
of iron. It can be used for cryogenic applications (1.2–300 K and even
up to 600 K). Both the sensitivity and the temperature range depends on
the iron concentration. The sensitivity is typically around 15 µV/K at
low temperatures and the lowest usable temperature varies between 1.2
and 4.2 K.
Type of Cables :
-
RT-2Y(St)Yv, RT-Y(St)Yv
-
RT-2Y(St)Yv PiMF, RT-Y(St)Yv PiMF
-
RT-2Y(St)YQY, RT-Y(St)YQY
-
RT-2Y(St)2YSWAY, RT-Y(St)YSWAY
-
RT-2Y(St)2YSWAY PiMF, RT-Y(St)YSWAY PiMF
Applicable Standards : IEC, DIN, VDE, ANSI, JIS,
CV.
MANDIRI KARYA BERSAMA
Kantor : Jl.
Moch Toha , Karawaci, Tangerang
Banten – Indonesia
PIN :
5C54D942 / 59574694
Telp. : 021 –
22252171
Hp : 082210137341,
081316684910, 0895333141311
Email contact
:
elinda.explosionproof@gmail.com
/ sales.mkb1@gmail.com / sales.mkb2@gmail.com
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